Amazon will allow Prime users to stream CBS' television content. The terms of the deal were not disclosed. According to The Street:

Starting this summer, Amazon will add 2,000 episodes to grow the total
number of Prime instant videos to more than 8,000 movies and television
shows, and offer full seasons for 18 popular television series,
including The Tudors, Numb3rs, Medium, the complete Star Trek franchise, Frasier and Cheers.

Amazon says the new titles will bring its streaming library up to 8,000
titles; Netflix boasts around 20,000 titles for its digital-only
library. For now, Amazon’s Web video titles are free to customers who
use its “Prime” delivery service, but industry observers assume that
library access will also be a big part of the new iPad-like tablet the
company is expected to unveil this fall.

Best-case digital scenario for big media players

AllThingsD continues that "the company gets to take old shows and resell them multiple times
(and maybe more, as Microsoft, Apple, and others eye the market), and
doesn’t have to worry about cannibalization.

Things get much trickier when consumers decide they want to watch
current programing, though. That stuff continues to be worth much more
to studios and networks when it runs on broadcast or cable TV, but
convincing viewers to play along is getting increasingly difficult."